The present invention relates to a fluid discharge method and a fluid discharge device required in such technical fields as information/precision equipment, machine tools, and FA (Factory Automation), or in various production processes of semiconductors, liquid crystals, displays, surface mounting, and the like.
For liquid discharge devices (liquid dispensers), which have hitherto been used in various fields, there has arisen a growing demand for a technique of feeding and controlling very small amounts of fluid material with high precision and high stability, against the background of recent years' needs for smaller-size electronic components and higher recording density. For example, in the fields of plasma displays, CRTs, organic EL, or other displays, there has been a great demand for direct patterning of fluorescent material or electrode material on the panel surface without any mask instead of conventional screen printing, photolithography, or other like methods.
Issues of dispensers for those purposes can be summarized as follows:
{circle around (1)} Scale-down of discharge amount,
{circle around (2)} Higher accuracy of discharge amount, and
{circle around (3)} Reduction of discharge time.
The machining accuracy in machining work has been moving from micron into submicron orders. Whereas submicron machining is commonly used in the field of semiconductor and electronic components, the demand for ultraprecision machining has been rapidly increasing also in the field of machining work that has been making progress along with mechatronics. In recent years, along with the introduction of the ultraprecision machining technique, electromagnetostriction devices typified by ultra-magnetostriction devices and piezoelectric devices have been coming to be applied to micro actuators.
With these electromagnetostriction devices used as the generation source for fluid pressure, there have been devised injection devices for injecting very small amounts of droplets at high speed in various fields.
For example, a method of injecting one arbitrary droplet with an ultra-magnetostriction device is disclosed in Japanese unexamined patent publication No. 2000-167467. Referring to FIG. 35, reference numeral 502 denotes a cylinder made of a nonmagnetic material such as glass pipe or stainless pipe. At one end portion of this cylinder 502 is formed an injection nozzle 504 having a liquid storage portion 503 and a minute injection port. Inside the cylinder 502, an actuator 505 made of a bar-shaped ultra-magnetostriction material is accommodated so as to be movable. A piston 506 is contactably and separably provided at an end portion of the actuator 505 suited for the injection nozzle 504.
Between the other end portion of the actuator 505 and a stopper 507 of the one end portion of the cylinder 502, a spring 508 is interposed so that the actuator 505 is biased by the spring 508 so as to be moved forward. Also, a coil 509 is wound at a position near the piston 506 on the outer periphery of the cylinder 502.
In an injection device having the above construction, a current is instantaneously passed through the coil 509 so that an instantaneous magnetic field acts on the ultra-magnetostriction material, by which an instantaneous transient displacement due to an elastic wave is generated at an axial end portion of the ultra-magnetostriction material. By the action, it is described, the liquid filled in the cylinder 502 can be injected from the nozzle 504 as one minute droplet.
As a fluid discharge device, conventionally, such a dispenser employing an air pulse system as shown in FIG. 36 has been widely used, and this technique is introduced, for example, in “Jidoka-Gijutsu (Mechanical Automation), Vol. 25, No. 7, '93.”
A dispenser of this system applies a constant amount of air supplied from a constant-pressure source into the interior 601 of a vessel (cylinder) 600 in a pulsed manner and then discharges from a nozzle 602 a certain amount of liquid corresponding to a pressure increase in the cylinder 600.
In the field of circuit formation, or in the fields of electrodes, ribs, and fluorescent-screen formation of PDP, CRT, or other image tubes, and manufacturing processes of liquid crystals, optical disks, or the like, where higher precision and higher micro-fineness have been increasingly demanded for those fields in recent years, the fluid material to be micro-finely discharged is high-viscosity powder and granular materials in many cases.
It is the greatest issue how those powder and granular materials containing fine particles can be discharged onto the object substrate at high speed and high precision and without causing clogging of flow passages and moreover with high reliability.
With regard to the fluorescent material-layer forming process of plasma display panels as an example, issues of the prior art are described below.                [1] Issues of the screen printing method and the photolithography method        [2] Issues in direct patterning of a fluorescent material layer by a conventional dispenser technique First, issue [1] is explained.(1-1) Construction of Plasma Display Panel        
FIG. 34 shows an example of the construction of a plasma display panel (hereinafter, referred to as PDP). The PDP is composed roughly of a front side plate 800 and a rear side plate 801. A plurality of sets of linear transparent electrodes 803 are formed on a first substrate 802, which is a transparent substrate forming the front side plate 800. Also, on a second substrate 804 forming the rear side plate 801, a plurality of sets of linear electrodes 805 are provided parallel to one another so as to be perpendicular to the linear transparent electrodes. These two substrates are opposed to each other with interposition of barrier ribs 806 on which the fluorescent material layer is formed, and then discharge gas is sealed into the barrier ribs 806. When a voltage not lower than the threshold is applied to between the electrodes of the two substrates, electric discharge occurs at the positions where the electrodes perpendicularly cross each other, causing discharge gas to emit light, where the light emission can be observed through the transparent first substrate 802.
Then, controlling the discharge positions (discharge points) allows an image to be displayed on the first substrate side. For color display by PDP, fluorescent materials which emit light of desired colors by ultraviolet rays radiated upon discharge at individual discharge points are formed at positions corresponding to the discharge points (partition walls of barrier ribs), respectively. For full-color display, fluorescent materials for R, G, and B, respectively, are formed.
The constitution of the front side plate 800 and the rear side plate 801 is explained in more detail.
As to the front side plate 800, a plurality of sets of linear transparent electrodes 803, each one set comprising two electrodes, are formed from ITO or the like, parallel to each another, on the inner surface side of the first substrate 802 formed of a transparent substrate such as a glass substrate. Bus electrodes 807 for reducing the line resistance value are formed on the inner-side surfaces of these linear transparent electrodes 803. A dielectric layer 808 for covering those transparent electrodes 803 and bus electrodes 807 is formed all over the inner surface of the front side plate 800, and a MgO layer 809 serving as a protective layer is formed all over the surface of the dielectric layer 808.
On the other hand, on the inner surface side of the second substrate 804 of the rear side plate 801, a plurality of linear address electrodes 805 which perpendicularly cross the linear transparent electrodes 803 of the front side plate 800 are formed in parallel from silver material or the like. Also, a dielectric layer 810 for covering those address electrodes 805 is formed all over the inner surface of the rear side plate. On the dielectric layer 810, the address electrodes 805 are isolated and moreover the barrier ribs (partition walls) 806 of a specified height are formed so as to protrude between the individual address electrodes 805 for the purpose of maintaining the gap distance between the front side plate 800 and the rear side plate 801 constant.
With these barrier ribs 806, cells 811 are formed along the individual address electrodes 805, and fluorescent materials 812 of respective R, G, and B colors are formed one by one in the inner surfaces of the cells 811. The PDP in cell structure comes in two types, one in which such discharge points as shown in FIG. 34 are provided one in each one independent cell and the other in which the discharge points are partitioned by partition walls on an array basis (not shown). In recent years, the “independent cell system” has been drawing attention as a system that allows performance improvement of PDPs.
The reason for this is that enclosing the cell with four-side barrier ribs in a waffle-like state makes it possible to prevent optical leakage between adjoining cells as well as to increase the area of the light emitter. As a result, the luminous efficiency and the emission amount (brightness) are increased so that a high-contrast image can be implemented, which is regarded as a characteristic of the “independent cell system”.
The fluorescent material layer formed on the cell wall surfaces is deposited generally to a thickness of about 10-40 μm with a view to a better coloring property. For the formation of the R, G, and B fluorescent material layers, a fluorescent-material coating liquid is filled into each cell and thereafter dried, thereby removing volatile components removed, by which a thick fluorescent material is formed on the cell inner surface while a space for filling with discharge gas is formed at the same time. In order to form such a thick-film fluorescent-material pattern, the coating material containing a fluorescent material is prepared as a reduced-in-solvent-quantity paste fluid (fluorescer-member use paste) having a high viscosity of several thousands of mPa·s to several tens of thousands of mPa·s and, conventionally, applied to the substrate by screen printing or photolithography.
(1-2) Issues of the Conventional Screen Printing Method
With the conventional screen printing method adopted, a large-scaled screen size would cause a large elongation of the screen plate due to tensile force, making it harder to achieve high-precision alignment of the screen printing plate for the whole screen. Also, in filling with the fluorescent material, the material might be placed even on the top portions of the partition walls, which would lead to crosstalk between barrier ribs as a problem in the case of the “independent cell system”. As a result of this, it has been necessary to take measures such as introduction of a polishing process for removing the material deposited on the top portions of the partition walls. Further, since the amount of filled fluorescent material varies depending on the difference in squeegee pressure, pressure control therefor is extremely subtle work, which largely depends on the degree of the skill of the operator. Thus, it is quite hard to obtain a constant filling amount for every independent cell over the entire rear side plate.
(1-3) Issues of Conventional Photolithography
Conventional photolithography has had the following issues. In this method, a photosensitive fluorescent-material paste is press-fitted into the cells between the ribs, and then only the photosensitive composition that has been press-fitted into specified cells is left through the exposure and development processes. Thereafter, through a baking process, organic matters in the photosensitive composition are dissipated, by which a fluorescent material-layer pattern is formed. In this method, in which the paste in use contains fluorescent-material powder so that the method is low in sensitivity to ultraviolet rays, there has been difficulty in obtaining a 10 μm or more film thickness of the fluorescent material layer. Thus, the method has had an issue that enough brightness cannot be obtained.
Also, in the case where photolithography is adopted, exposure and development processes are essential for each color. However, since the fluorescent material is contained in the paste coating layer at high concentration, the loss of the fluorescent material due to the development removal is so large that the effective utilization ratio of the fluorescent material is a little less than 30% at most. Thus, there has been a large issue in terms of cost. [2] Issues in direct patterning of a fluorescent material layer by a conventional dispenser technique
Conventionally, an attempt is made that discharging of the imaging tube is performed by using an air nozzle-type dispenser (FIG. 36) which is widely used in the fields of circuit mounting and the like. Since continuous discharge with high-viscosity fluid at high speed is difficult to do with the air nozzle-type dispenser, fine particles are diluted with a low-viscosity fluid before being discharged. In the case of fluorescent-material discharge on PDP, CRT, or other image tubes, the particle size of fine particles is 3 to 9 μm as an example and their specific gravity is about 4 to 5. In this case, there has been an issue that when the fluid flow is stopped, the fine particles would be immediately deposited inside the flow passage due to the weight of a single particle.
Furthermore, a dispenser of the air type has had a drawback of poor responsivity. This drawback is due to the compressibility of air entrapped in the cylinder as well as to the nozzle resistance during the passage of air through narrow gaps. That is, in the case of the air type, the time constant of the fluid circuit that depends on cylinder volume and nozzle resistance is such a large one that a time delay of about 0.07 to 0.1 second has to be allowed for after an input pulse is applied until the fluid is started being discharged and further transferred onto the substrate.
The discharge device using as the drive source a piezoelectric material or ultra-magnetostriction material as described before in FIG. 35 is a proposal targeted for discharge of fluid containing no powder, and it is predicted to be difficult to respond to the aforementioned challenge related to the discharge process of powder and granular materials. Also, in the case where a fluid is discharged by using instantaneous transient displacement due to elastic waves, the liquid storage portion 503 has to be normally filled with the fluid without gaps, where the volume is constant. There is no description as to how the fluid is supplied to the liquid storage portion 503 in order to replenish the fluid that is consumed on and on as time elapses.
There has been development being made for applying ink jet type dispensers, which have been widely used as consumer printers, to discharge devices for industrial use. The ink jet type dispensers, for which the viscosity of the fluid is limited to 10 to 50 mPa·s from the restrictions of drive method and structure, are incapable of treating high-viscosity fluids.
In order to draw a fine pattern by using an ink jet type dispenser, there has been developed a low-viscosity nano-paste in which particles having a mean particle size of about 5 nm and covered with a dispersant are independently dispersed. Now a case is assumed where the fluorescent material layer is formed on the inner walls of the barrier ribs (partition walls) of the PDP as described above by using this nano-paste. However, in the process of filling the fluorescent-material-use-coating liquid into the cells and then drying it, a reduced-in-solvent-quantity paste fluid having a high viscosity is conventionally used as the coating material containing fluorescent material in order to deposit a fluorescent material layer thick to a thickness of about 10-40 μm as described above. With a low-viscosity nano-paste, which is only capable of providing a lean content of fluorescent material, the absolute quantity of the fluorescent material lacks so that the fluorescent material layer of a specified thickness could not be formed.
Also, whereas fluorescent-material fine particles whose particle size is on the order of several microns are generally regarded as optimal for the display to obtain high brightness, it is also a large issue for ink jet type dispensers that the fluorescent-material particle size cannot be easily changed as it stands.
In summary of the above discussions, there cannot be found, for the present, any engineering method having a capability of substituting for the screen printing method and the photolithography method, for example, a direct patterning method that implements the formation of the fluorescent material layer for the independent cells of PDPs.
In order to meet recent years' various requests related to the minute-flow-rate discharge of fluid and powder and granular materials, the present inventor has proposed and applied for a patent for a discharge method for controlling the discharge amount, “Fluid Feeding Device and Fluid Feeding Method” (Japanese unexamined patent publication No. 2002-1192) (U.S. Pat. No. 6,558,127), in which, with relative linear motion and rotational motion between a piston and a cylinder, fluid conveying means is implemented by the rotational motion while a relative gap between the fixed side and the rotating side is changed by using the linear motion.
Further, the inventor has already proposed an intermittent discharge method and device which utilizes a squeeze effect which is generated by abruptly changing the gap between a piston end face and its relatively moving surface on the basis of a theoretical analysis performed on the dispenser structure disclosed in the foregoing proposal (Japanese unexamined patent publication No. 2002-301414)(U.S. Pat. No. 6,679,685).
As a result of following stricter theoretical analysis, the present inventor has found that devising a combination of pump characteristics and piston makes it possible to obtain a generated pressure (secondary squeeze pressure) equal to or higher than the squeeze effect even with a sufficiently wide gap between the piston end face and its relatively moving surface. The present inventor has already proposed an ultrahigh-speed intermittent discharge device which, it is claimed as implementable, is easy to handle in practical use, high in flow-rate precision and high in reliability to powder and granular materials on the basis that only simple control of the gap of the piston end face is required and the total discharge amount per dot can be set by the pump rotating speed by virtue of the above-described effect (Japanese patent application No. 2003-341003 which was published as Unexamined Japanese Patent Publication No. 2004-141866) (U.S. patent application Ser. No. 10/673,495).
In the present invention, as a result of further research under strict comparisons with experimental results, it has been found on the basal steps of the above-described proposals that the compressibility of the fluid has a large effect on the generation of the squeeze pressure. Here is proposed a head structure that implements high-speed intermittent, high-speed continuous discharge on the basis of the findings obtained from analytical results derived in consideration of the compressibility.